2041 大気乱流拡散に関する風洞実験

Abstract

Experiments on particle diffusion were conducted under different turbulent Reynold's numbers (Re_λ≒35&acd;550) in a wind tunnel with an active turbulence generator. Mean concentration properties of the particle diffusion were compared between the excited turbulence (Re_λ≒550) and the grid turbulence (Re_λ≒35). A double tubular injection nozzle employed to reduce the velocity defect of the wake behind it. The mean concentration profiles were nearly Gaussian and it's plume mean width develops downstream as described by the Taylor's theory. In the excited turbulence where plume meandering motion dominated, the diffusion field was short-time diffusion (T<T_L). In the grid turbulence where only relative diffusion occurs was the long-time diffusion (T>T_L). These results assured the reliability of Taylor's diffusion theory. The diffusivity, K, reached about 110(cm)^2/s in the excited turbulence and is far larger than the value obtained in the grid turbulence (K≒7(cm)^2/s). The results of the experiments showed that the diffusion mechanism was examined in more detail by controlling of the background turbulence characteristics.